The invention relates to a steering wheel for motor vehicles, consisting of a pot-shaped lower part and an upper part connected thereto along its edge side, both parts having an outer shell of high-performance plastic material. Such a steering wheel is known from DE-A-21 29 286, for example.
Steering wheels for motor vehicles consist generally of a metallic steering wheel carcass, a casing of foamed plastic material having a leather-like outer skin and an airbag housed in the steering wheel and having a cover visually and haptically adapted to the outer skin of the steering wheel. The carcass may consist of steel, aluminum, magnesium or combinations of these metals and is designed such that it can transmit all forces occurring while driving. Furthermore, today""s steering wheels are often still designed in such a way that they can deform specifically during an accident when the drier strikes the steering wheel. Together with the abruptly inflating airbag the forces acting upon the casualty shall be reduced by this and injuries shall be reduced and prevented in the optimum case.
The production of such steering wheels is relatively complicated because in addition to the line for producing the metallic carcasses a second production line must be established for sheathing the carcasses with a suitable, foamable plastic material forming a tight, abrasion-resistant outer skin. If the steering wheel carcasses are made by casting, they will have to be freed from nipples or flashes before they can be inserted in the mold to be sheathed with plastics. Steering wheels which consist of prefabricated hubs, spokes and steering wheel rims require additional riveting, bolting or welding steps until a carcass ready for sheathing exists.
In addition to the expenses regarding product engineering it is considered disadvantageous in connection with conventional steering wheels that the case as such already offers a certain impact protection because the supporting steering wheel carcass is covered at least in all impact areas but does not make a contribution to the structural strength of the steering wheel. This strength has to be achieved by a corresponding cross-sectional design of the steering wheel carcass so that narrow limits are set to the general striving for weight reduction in motor vehicles even if aluminum or magnesium alloys are used.
U.S. Pat. No. 5,649,455 discloses an energy-absorbing element which is attached to a steering wheel hub and has honeycomb webs.
The object of the invention is to provide a steering wheel which enables further savings of weight without limiting its functions as regards the transmission of forces occurring while driving and as regards the impact protection.
In order to achieve this object it is proposed according to the invention that in a steering wheel of the initially mentioned kind at least the outer shell of the lower part is reinforced by webs pointing inwards and being molded on integrally, which webs plastically deform in an impact with taking up strain energy.
The invention is based on the consideration that a steering wheel carcass can be dispensed with when suitable high-performance plastic materials are used and by corresponding fashioning care is taken that said main functions can be met sufficiently. In addition, the change from carcass to shell design has the further advantage that less material expense is required to achieve certain strength values with equal materials because the supporting material can be utilized much better in terms of strength when it is disposed in the outer regions of a component. impact protection can also be obtained.